Calcification of the oral microorganism Bacterionema matruchotii (Ennever et al., 1976, human dental calculus (Ennever et al., 1977), marmoset bone (Ennever et al., 1977) and chick epiphyseal cartilage (Boyan-Salyers et al., 1979) are proteolipid dependent, i.e., extraction of proteolipid from these matrices renders them noncalcifiable. Proteolipids which will support in vitro apatite formation have also been isolated from non-calcifying tissues and from tissues not known to calcify (Boyan-Salyers et al., 1978) suggesting that in vivo proteolipid initiation of calcification is subject to cellular regulation. The purpose of the proposed reseach is to examine the role of proteolipid in biologic calcification by identifying factors which influence proteolipid initiation of apatite formation. Epiphyseal cartilage will serve as a model for examining proteolipid chemistry during progressive mineralization and in response to vitamin D. The relationship between matrix vesicle proteolipid (MVP) and the cartilage cell will be established biochemically, immunohistochemically, and enzymatically. Membrane requirements for calcification will be identified by investigating the spatial relationship of MVP in the matrix vesicle membrane.